1. Field of the Invention
The present invention generally relates to solid state amplifiers and fixtures for testing solid state devices and, more particularly, to spatial-power-combined amplifiers which use multiple cards or arrays of solid-state amplifiers and radiating antennas and, at the same time, incorporate the ability to act as a flexible test fixture.
2. Description of Related Art
The use of solid-state power combining amplifier techniques has continued to be of interest because of considerations pertaining to size, weight, reliability and manufacturing cost. In the context of microwave/millimeter-wave systems, for example, power combining amplifier techniques are of significance since those systems potentially provide larger output power than a single solid-state amplifier. Further, those types of systems are readily adaptable to changes in the physical and geographical environment. And, the interest in microwave/millimeter-wave systems spans a wide range of applications, including military applications such as radar, missile seekers, satellite links, and consumer applications such as base stations for wireless communications.
In an application where a large number of microwave/millimeter-wave amplifiers must be combined, conventional power combining amplifier techniques have performed at lower than optimal levels. One conventional technique has been referred to as the corporate combiner. Multiple solid-state amplifiers are successively combined using two-way adders. But as the number of amplifiers becomes large, the power combining efficiency can become too low. Other contributing factors to decreased efficiency are resistive, radiative, and dielectric losses.
Another conventional technique is the chain combiner. An input waveguide feeds all of the amplifier inputs, and all of the amplifier outputs feed an output waveguide. Cross-guide couplers with adjustable coupling ratios at each amplifier stage are used to ensure an equal power distribution to the amplifiers on the input waveguide.
In an effort to address some of the performance concerns in conventional techniques, new power combining methods using spatial or quasi-optical techniques have been developed. Those techniques are an extension of classical antenna array systems. The techniques generally incorporate a planar array of cells, each having a conventional planar antenna structure. The cells are usually a half-wavelength or larger in size and the array is placed in a radiating structure. Most often, the array is positioned transverse to the propagating beam. Thereby, the array couples energy from the multiple devices in free-space or in a metallic waveguide. Among other things, what is sought is a reduction in diffraction losses and more power in a smaller volume.
Yet, in the past, optimization of spatial-power-combined amplifiers using metallic waveguides has been limited for various reasons. For example, the maximum achievable power is derived from the efficiency of the amplifier as a whole rather than the power per device. Therefore, power can be increased by increasing the device density or overall size of the amplifier array. But as the density of the devices increases or the size of the array increases, the need to remove heat increases. As can be appreciated, the increased need to remove heat places a limitation on the maximum density or size of array achievable. Additionally, the individual amplifiers must be supplied with a bias. Preferably, the bias is supplied in such a fashion that the failure of one device does not affect all of the others. But, again, as the device density and/or array size increases, the supplying of a bias becomes more problematic. When spatial power combining techniques have incorporated multiple arrays to achieve higher power amplification with higher gain and efficiency, the above issues have become greater, as well as usability issues arising. Therefore, with the possibility of less than optimal performance, there is a need to efficiently and quickly evaluate potential amplifier card configurations in a spatial-power-combined amplifier.
In an effort to meet the objectives of evaluating and optimizing solid state devices and monolithic microwave integrated circuits (MMICs), Wiltron Co. has produced a universal test fixture for testing a single substrate of either microstrip or coplanar waveguide circuits. A fixed connector block allows a jaw to clamp one end of the substrate. A sliding connector block can slide into connection with another end of the substrate. A connector pin from the jaw connects with a substrate conductor. With the ability to hold only a single substrate, it can be appreciated that efficiency of use of such device is less than if multiple substrates could be held for evaluation at any given time.
As can be seen, there is a need for improved spatial power combining apparatus and, in particular, a spatial-power-combined amplifier in a metallic waveguide that provides for the use of multiple amplifier device arrays which remain easily changeable from one array to another to thereby increase the efficiency in use and number of useful environments. At the same time, there is a need to have the spatial-power-combined amplifier serve as a fixture to test amplifier devices found in the arrays.